The present invention relates to a cylinder apparatus and a disk brake.
As an example of a cylinder apparatus in which a piston slidingly moves in a cylinder, there is known a disk brake wherein a braking operation is effected by causing a piston to slidingly move in a cylinder under application of a hydraulic pressure, whereby the piston is pushed outward relative to the cylinder against a brake pad, which in turn is brought into contact with a brake disk. To facilitate a process of forming an interior of a cylinder of such a disk brake, a cylinder may be divided into a covering member, which is provided in a bottom portion of the cylinder, and a cylinder body that has an opening which is closed by the covering member. In using this configuration, a process of forming an interior of the cylinder body is performed through the opening, after which the covering member is attached to the cylinder body so as to close the opening. Attachment of the covering member is effected by screwing the covering member into the opening of the cylinder body (refer to, for example, Japanese Utility Model Public Disclosure No. HEI 05-64542 and Japanese Utility Model Public Disclosure No. HEI 06-69456).
However, in a connecting structure such as that of the above-mentioned cylinder, in which a cover member is screwed into an opening of a cylinder body, it is necessary to form a male thread on the covering member and a female thread on the cylinder body. Further, it is also necessary to form a tool-attaching portion such as a hexagonal socket for applying a force to the covering member to connect it to the cylinder body. To ensure sufficient strength, when a tool-attaching portion such as a hexagonal socket is employed, it is necessary to increase a thickness of the covering member. Further, it is necessary to form threads and a seal groove. As a result, an axial dimension of the cylinder increases. In employing such a configuration, it is also necessary to provide the covering member or the cylinder body with a seal ring for sealing a gap between the covering member and the cylinder body. Provision of the seal ring necessitates formation of a seal groove for holding the seal ring. This significantly increases processing costs. Further, use of a seal ring causes an increase in an overall number of parts used, and, therefore, a corresponding increase in parts' costs. Further, use of a seal ring gives rise to a danger of fluid loss (fluid leakage) due to elastic deformation or the like of the seal ring. These problems relate not only to disk brakes, but also to a variety of other cylinder apparatuses in which a structure is employed wherein an opening of a cylinder body is closed by a covering member.
Therefore, an object of the present invention is to provide a cylinder apparatus and a disk brake wherein although an opening of a cylinder body is closed by a covering member, the cylinder apparatus and disk brake are leak proof and can be reduced in size, and processing and parts' costs are also kept low.